The present invention relates to a web crushing arrangement for a card web having cooperating working rolls, with a support member extending along one of the rolls for taking up the pressing surface, which is pressable against the roll by pressure bodies, as used in staple fibre spinning, and more particularly, in processing natural fibres.
Crushing a very thin fibre web, such as it is taken off from the doffer cylinder of a card, has as its purpose reducing the impurities, mainly the harder seed particles, by crushing them in such a manner that they impair the subsequent processing stages to a lesser degree. They also can be eliminated from the fibre material more easily.
For achieving good results using a web crushing arrangement of this type, the uniformity of the crushing pressure generated along the full working width of the roll, which is of the order of about 1 m, is of decisive importance. If the pressure is too low, the impurities are not crushed, or are not crushed sufficiently, i.e. the crush roll arrangement does not achieve the desired effect; whereas too high pressures result in damage to the fibre material. For evenly loading the crush rolls many efforts have been undertaken already; however, these have resulted in proposed solutions which are still unsatisfactory.
According to a known web crushing arrangement of the aforementioned type (German Patent PS 904'150), a uniform pressure distribution with two working rolls supported along their length is achieved by each working roll being supported on its working surface by at least one pressure-loadable support member; the support member preferentially being designed as a member of uniform stiffness.
In a further development of this solution (German Patent PS 918'676), design of the pressure transmitting element arranged between the working roll and the support member as an elastic element is also known.
The disadvantage of this crush roll arrangement is that the rotating crush roll, with its cylindrical surface, is in frictional contact with the pressure loaded support member, or with the pressure transmitting element, respectively, under the full pressure force. This causes a corresponding energy loss and presents considerable danger of damage, or of excessive wear, respectively, to the very susceptible roll surface, which, in turn, causes increased danger of lap-up formation on the working roll.
Also, maintenance and operating work on such web crushing arrangements are increased due to excessive danger of lap-formation.